git: dfb4fb41166b - stable/13 - libpmc: fall-back to kernel tables if pmu-events fails

[Mitchell Horne]

The branch stable/13 has been updated by mhorne:

URL: https://cgit.FreeBSD.org/src/commit/?id=dfb4fb41166bc35935e5f6fd9351a0ada0f71159

commit dfb4fb41166bc35935e5f6fd9351a0ada0f71159
Author:     Mitchell Horne <mhorne at FreeBSD.org>
AuthorDate: 2021-05-13 18:57:37 +0000
Commit:     Mitchell Horne <mhorne at FreeBSD.org>
CommitDate: 2021-07-29 15:01:09 +0000

    libpmc: fall-back to kernel tables if pmu-events fails
    
    On x86, the pmu_events table is the source of truth for finding
    supported events. However, events not found there may still be present
    in the kernel's static event tables. For example, the pmc.soft(3) events
    will never be available from pmu-events.
    
    Update pmc_allocate() to search the legacy event tables if
    pmc_pmu_pmcallocate() fails to return a result. This allows both event
    sources to be consulted before giving up, thus restoring pmc.soft(3) and
    pmc.tsc(3) on x86.
    
    Reviewed by:    emaste
    MFC after:      2 weeks
    Sponsored by:   The FreeBSD Foundation
    Differential Revision:  https://reviews.freebsd.org/D30216
    
    (cherry picked from commit dfdc57e8aa8ba4b4e4484f736e8c7645ab69b54a)
---
 lib/libpmc/libpmc.c | 40 +++++++++++++++++++---------------------
 1 file changed, 19 insertions(+), 21 deletions(-)

diff --git a/lib/libpmc/libpmc.c b/lib/libpmc/libpmc.c
index 6636c974cb73..e2422f167267 100644
--- a/lib/libpmc/libpmc.c
+++ b/lib/libpmc/libpmc.c
@@ -989,25 +989,25 @@ pmc_allocate(const char *ctrspec, enum pmc_mode mode,
 	pmc_config.pm_count = count;
 	if (PMC_IS_SAMPLING_MODE(mode))
 		pmc_config.pm_caps |= PMC_CAP_INTERRUPT;
+
 	/*
-	 * Can we pull this straight from the pmu table?
+	 * Try to pull the raw event ID directly from the pmu-events table. If
+	 * this is unsupported on the platform, or the event is not found,
+	 * continue with searching the regular event tables.
 	 */
 	r = spec_copy = strdup(ctrspec);
 	ctrname = strsep(&r, ",");
 	if (pmc_pmu_enabled()) {
-		if (pmc_pmu_pmcallocate(ctrname, &pmc_config) == 0) {
-			if (PMC_CALL(PMCALLOCATE, &pmc_config) < 0) {
-				goto out;
-			}
-			retval = 0;
-			*pmcid = pmc_config.pm_pmcid;
-			goto out;
-		}
-		errx(EX_USAGE, "ERROR: pmc_pmu_allocate failed, check for ctrname %s\n", ctrname);
-	} else {
-		free(spec_copy);
-		spec_copy = NULL;
+		if (pmc_pmu_pmcallocate(ctrname, &pmc_config) == 0)
+			goto found;
+
+		/* Otherwise, reset any changes */
+		pmc_config.pm_ev = 0;
+		pmc_config.pm_caps = 0;
+		pmc_config.pm_class = 0;
 	}
+	free(spec_copy);
+	spec_copy = NULL;
 
 	/* replace an event alias with the canonical event specifier */
 	if (pmc_mdep_event_aliases)
@@ -1064,14 +1064,12 @@ pmc_allocate(const char *ctrspec, enum pmc_mode mode,
 		goto out;
 	}
 
-	if (PMC_CALL(PMCALLOCATE, &pmc_config) < 0)
-		goto out;
-
-	*pmcid = pmc_config.pm_pmcid;
-
-	retval = 0;
-
- out:
+found:
+	if (PMC_CALL(PMCALLOCATE, &pmc_config) == 0) {
+		*pmcid = pmc_config.pm_pmcid;
+		retval = 0;
+	}
+out:
 	if (spec_copy)
 		free(spec_copy);